The geophysical signature of a continental intraplate volcanic system: From surface to mantle source

• Published in: Earth and planetary science letters 2022-01, Vol.578, p.117307, Article 117307
• Main Authors: Comeau, Matthew J., Becken, Michael, Grayver, Alexander V., Käufl, Johannes S., Kuvshinov, Alexey V.
• Format: Article
• Language: English
• Subjects: alteration; electrical resistivity; intraplate volcanism; magma plumbing; mantle upwelling; partial melt
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2021.117307

•Electrical resistivity models image crust and mantle below intraplate volcanic zone.•Ancient magma pathways imaged in the crust possibly due to metasomatic alteration.•In the mantle, a potential zone of melt is detected that can be the magma source.•Models consistent with direct magma ascent from mantle and no crustal storage.•Cause of volcanism is attributed to a broad mantle upwelling and thermal anomaly. The structure of continental intraplate volcanic systems — which occur far from tectonic boundaries, unlike the majority of Earth's volcanism — is enigmatic and not fully understood, as are the underlying mechanisms responsible, due in part to a lack of high-resolution geophysical data. Central Mongolia contains Quaternary–Neogene aged alkaline basalt flows and volcanic cones, thousands of kilometres from active tectonic margins, in addition to an abundance of geochemical and petrological data — making this a natural laboratory to study intraplate volcanism. Using a recently collected, high-resolution, multi-scale, magnetotelluric dataset acquired across central Mongolia, we generate and analyze electrical resistivity models of the structure beneath the Tariat and Chuluut volcanic zones with the goal of imaging the volcanic system from surface to mantle source. The models reveal narrow, subvertical, lower resistivity anomalies in the middle-upper crust that are conspicuously located beneath surface expressions of volcanism. The lower crust (depths of 25–50 km) is characterized by the widespread distribution of isolated low-resistivity zones. A local low-resistivity zone is imaged in the mantle (depths of 60–90 km) above a broad, homogenous, doming low-resistivity feature. Considering the available evidence, we propose that the low-resistivity anomalies in the middle-upper crust are the remnant signatures of past transient magma pathways (or collection of pathways), caused by metasomatic alteration during the ascent of hot magmatic fluids. The lower crustal anomalies are interpreted to be domains of saline fluids in a thermally perturbed lower crust. In the mantle, the low-resistivity structure is explained by a broad mantle upwelling and thermal anomaly with a local zone of low-percent partial melt — the source for intraplate volcanism. The geophysical images are consistent with geochemical and petrological evidence from erupted lavas that indicates a single common mantle source region, limited crustal contamination, and rapid direct ascent, making cru